Emergent gravity from the IIB matrix model and cancellation of a cosmological constant

TL;DR

This paper discusses a cosmological model where the metric determinant influences the universe's evolution, showing how vacuum energy and a cosmological constant can cancel out, potentially solving the cosmological constant problem.

Contribution

It introduces a new cosmological model based on restricted coordinate invariance and links it to emergent gravity from the IIB matrix model, providing numerical evidence for vacuum energy cancellation.

Findings

Numerical results demonstrate cancellation of vacuum energy density.

Model's action is invariant under restricted coordinate transformations.

Nonstandard matter terms may originate from emergent gravity in the IIB matrix model.

Abstract

We review a cosmological model where the metric determinant plays a dynamical role and present new numerical results on the cancellation of the vacuum energy density including the contribution of a cosmological constant. The action of this model is only invariant under restricted coordinate transformations with unit Jacobian (the same restriction appears in the well-known unimodular-gravity approach to the cosmological constant problem). As to the possible origin of the nonstandard terms in the matter action of the model, we show that these terms can, in principle, arise from the emergent gravity in the IIB matrix model, a nonperturbative formulation of superstring theory.